1. Field
The instant invention relates to box culverts constructed of corrugated metal, especially steel and aluminum.
2. State of the Art
Box culverts are drainage structures fabricated from structural plate steel or aluminum wherein the culvert has a large width-to-height (span-to-rise) ratio. Corrugated metal box culverts approach the shape of a low, wide box. Corrugated metal sheets of shallow corrugation with the side sheets having the corrugations running vertically have been conventionally used for box culvert construction.
The shape of a box culvert has generally been dictated by its use, namely in situations where a roadway height above a stream bed, for example, was minimal, yet the culvert opening had to accommodate at least periodic flows of large volumes of water. Box culverts generally have dirt fill around their exterior surface with a minimal amount of fill above the culvert. In a true arch construction, the shape of the arch may deflect load from a roadbed above the culvert into the soil along the sides of the culvert. However, because of the width-to-height ratios, box culverts do not have the advantages of "true arch" construction. Also, because of the lack of stiffness in the sheet metal used in such box culverts, the primary support has been provided by the stiffening ribs, as illustrated in FIG. 1 and in U.S. Pat. No. 4,141,666 of DeGraff issued Feb. 27, 1974.
Box culverts traditionally have had a relatively flat top, typically having the shape shown in FIG. 1, labelled "Prior Art Box Culvert." Such a shape has necessitated the use of supplemental reinforcing members to support the top and sides of traditional box culverts.
In FIG. 1, corrugated metal plates were joined together to form the sidewalls 10, the roof 11 and corners 12 of a typical box culvert. Supplemental stiffening members or ribs 13 of thick cross-section and formed to have the predesigned cross-sectional shape of the box culvert were spaced along the length of the culvert to give the culvert the necessary strength to accept the magnitude and direction of applied loads. These supplemental ribs require field erection.
Cross-sections of rib stiffeners and typical haunch and crown stiffening members 13, often referred to as "ribs," are illustrated in FIGS. 2 and 3. Haunch ribs are located along the sides of the culvert while crown ribs are located over the top of the culvert. These particular ribs have been used especially with box culverts constructed from corrugated aluminum sheets. The shape and length of stiffening ribs render them inflexible. They are preformed to a particular length and curvature. Generally, one type of haunch rib can be adapted to several sizes (widths and heights) of box culverts since the same curved corner (same radius and radians) is present.
The necessity of supplemental stiffeners generally complicates erection of box culvert structures in the field, requiring additional time and labor. The metal sheets must be bolted together to form the basic structure, then the ribs must be bolted in place, using many bolts per rib, to form a rigid structure. The number of ribs per unit length must be increased as the width of a box culvert increases. When the width (span) and height (rise) increase to an extent that the shape (curvature) or length of arc of the corner changes, the shape and size of the rib also changes. Thus, a variety of ribs must be made, in order-to accommodate a wide variety of box culvert widths and heights.
While the structure illustrated in FIGS. 1-3 are typical for corrugated aluminum, corrugated steel structures are similarly constructed, i.e., from corrugated steel sheets and stiffener ribs. Stiffening ribs of steel may have a cross-section different than those shown in FIGS. 2 and 3, for example, angle iron may be used, however, a generally "L"-shaped cross-section is typical.
The structure illustrated in FIGS. 1 through 3 are similar to those contained in U.S. Pat. No. 4,141,666 of DeGraff which describes elongated stringers which run the length of the culvert and curved stiffening ribs. This reinforced structure was designed to replace low-headroom culverts having floors tying the lower edges of the culvert sidewalls together.
The structure illustrated in the DeGraff patent is particularly well suited for corrugated aluminum sheets. The patent indicates at column 4, lines 13, et seq. certain preferred aluminum alloys. While the DeGraff structure may function as desired, the structure requires considerable field erection and specialized reinforcement members.
While both aluminum and steel sheets with standard corrugations, respectively about 21/2".times.9" and 2".times.6" corrugations, have been used in conjunction with stiffeners to form the box culverts, specially corrugated, thick steel sheets have been used to form box culverts of the shape illustrated in FIG. 4 (prior art structure) without any stiffening ribs. The corrugated sheet steel has deep, approximately 5", corrugations with 15 inch spacing (pitch). The corner is sharp, i.e. a substantially square corner. Such a structure requires that the side sheet members be welded to the roof members. Such a structure has not required stiffening ribs; however, it has a bending moment profile of a less desirable shape (shown in dotted lines on FIG. 4), which has discouraged widespread use of such structures.
The shape of the culvert in FIG. 4 generally requires that the sidewalls of the culvert support loads applied to the roof without the benefit of much soil support.
A prior art box culvert structure employing stiffener ribs and stringers is illustrated and described in U.S Pat. No. 4,141,666.